Roku makes more from advertising than hardware sales.
There is already advertising on Amazon Fire, have you seen the Ads for NFL or Amazon originals like Jack Ryan or Mrs Maisel before your selected program starts?
Fire Stick market share is growing at 27%, it is within 5% of Roku. Think about all the consumer data Amazon has. They know how I shop, How often I browse before I purchase, what and when I buy. Wow this could be LARGE :). more here https://bit.ly/2T24UML and link to Business Insider article